Apparatus for screen printing



Dec. 17, 968 D. L. MILLER ETAL 3,416,440

APPARATUS FOR SCREEN PRINTING Filed March 18, 1966 8 Sheets-Sheet 1 a L l 5 cu $3 I m B :5 Q g 3 1 3n n g to J 8 s2 3 (D 1m 8 m M 9 mi s g o :I O 0 n2 o 4 P INVENTORS E DONALD L. MILLER GERARD J SPILLMAN AMES D. WHARMBY EDWARD J. STDKOWSKI JR.

Dec. 17, 1968 D. 1.. MILLER NETAL 3,416,440

APPARATUS FOR SCREEN PRINTING Filed March 18, 1966 Y 8' Sheets-Sheet 2 FIG. 2

7, 1968 D; L. MILLER ETAL 3,

APPARATUS FOR SCREEN PRINTING a Sheets-sheaf 4 Filed March 18, 1966 Dec. 17, 1968 n. MILLER ETAL 3,416,440

APPARATUS FOR SCREEN PRINTING Filed March 18, 1966 8 Sheets-Sheet 5 c- 17,1968 V D. L; MILLE AL g 3,416,440 I v a APBAYRATUSWFORISCREEK Paimme. Filed march 18, 1966' I a Shets-Shee t a 1968 D. 1.. MlLLER ETAL APPARATUS FOR SCREEN PRINTING 8 Sheets-Sheet 7 Filed March 18, 1966 Dec. 17, 1968 D. I MILLER ETAL 3,416,440

APPARATUS FOR SCREEN PRINTING 7 Filed March 18, 1966 8 Sheets-Sheet a CAM TIMING CHART WORKHOLDER 24 180 CLAMP ARMS (UNLOAD) 90 50 I OPEN CLOSED WORKHOLDER 7 240 b PEDESTAL (UNLOAD) I o d o .114 v 215 v TOPEN WORKHOLDER 2 265 CLAMP ARMS (LOAD) I CLOSED 90 210 WORKHOLDER PEDESTAL Dow" (LOAD) I49" f 201 SCREENING 2 549 P INKWELL 1940 ME I U II0IIIII 184 s09" m g 0 s49" INDEX LOCK LOCKED MECHANISM OUT 0 h j f IIovIIIc 5 INDEX DRIVE A STOP FIG. 17

i 2' DOWN 151 5 9' LOAD PLUNGER UP United States Patent 3,416,440 APPARATUS FOR SCREEN PRINTING Donald L. Miller and Gerard J. Spillman, Poughkeepsie,

Edward J. Stokowski, Jr., Wappingers Falls, and James D. Wharmby, Poughkeepsie, N.Y., assignors to International Business Machines Corporation, Armonk,

N.Y., a corporation of New York Filed Mar. 18, 1966, Ser. No. 535,384 17 Claims. (Cl. 10135) ABSTRACT OF THE DISCLOSURE The printing apparatus has a turret, a workpiece holder on the turret, a loading station, a printing station and a discharge station arranged about the turret. Workpieces are loaded at the loading station on the turret so that the upper surface of the workpiece is maintained at a predetermined reference plane. This plane is maintained, irrespective of variations in workpiece thickness by suitable workpiece holders on the turret. At the printing station, the printing mechanism is mounted on flexible straps to pivot into and out of printing position. Precise control of the plane of the upper surface of the workpiece and the printing position of the printing mechanism results in consistently uniform thicknesses of printed matter,

This invention relates to printing apparatus, more particularly to an apparatus for screen printing electrical circuit patterns, resistors, coatings, etc., in the manufacture of electrical components. Still more specifically, this invention relates to printing apparatus for automatically applying print designs to workpieces at high volume rates.

Economic considerations in general require modern mass production techniques to be applied to the manufacturing of goods for the mass market. These considerations exist in the electronic industry where competition necessitates that electronic components be produced at minimum cost. Many techniques have been developed to eliminate as much as possible the tedious manual operations formerly associated with this industry. Such techniques include the printing of circuits, resistors, capacitors, etc.

Automatic apparatus to print circuit resistors, capacitors, circuit patterns and the like are known in the art. However, these apparatus have not been capable of producing electrical elements and circuits that meet the desired tolerance standards. As the electronic circuitry becomes more miniaturized, and the performance standards are increased, the precision in printing becomes more and more essential. For example, in the printing of resistors, the resistor must not only be very precisely located on the workpiece, but also the thickness of the applied coating must be uniform throughout each individual resistor and consistent with other resistors on the same workpiece and also on other work-pieces. The same criteria applies to dielectric coatings in capacitors, and to a somewhat lesser extent to conductive land patterns.

Further, electronic circuits are frequently disposed on relatively small and fragile ceramic plates having a width and a length on the order of one-half inch and a thickness on the order of 0.060 inch. These plates, or workpieces, are referred to as substrates. Ceramic substrates can be slightly warped and/or vary in thickness, Prior art printing apparatus are not capable of printing patterns etc. on such substrates while maintaining the necessary and/ or desirable tolerances. These known apparatus are particularly deficient in maintaining uniform coating thicknesses of the pattern being printed, particularly When the substrates or workpieces are warped or vary in thickness from the standard.

An object of this invention is to provide a new and improved printing apparatus for automatically printing workpieces.

Another object of this invention is to provide an improved printing apparatus wherein workpieces to be imprinted are precisely and accurately located relative to a printing screen.

Yet another object of this invention is to provide a new printing apparatus that precisely locates the surface of the workpiece to be printed relative to the printing screen.

Another object of this invention is to provide a printing apparatus that is capable of repeatedly and consistently printing patterns on workpieces to close tolerances.

Yet another object of this invention is to provide a printing apparatus capable of printing workpieces in which the pattern printed is of a consistent, uniform thickness.

Yet another object of this invention is to provide a new printing apparatus provided with a means to precisely locate a workpiece surface to be printed at a predetermined reference plane, and a workpiece holder to support said workpiece at the elevation.

Yet another object of this invention is to provide a printing apparatus that is simple and dependable in operation.

Another object of this invention is to provide a printing apparatus capable of accurately and precisely screen printing a pattern on workpieces at a high volume rate.

Another object of this invention is to provide an automatic printing apparatus which gently handles and conveys workpieces to be printed through the various work stations.

Another object of this invention is to provide a printing apparatus having a workpiece removal means at the discharge station that gently removes the workpieces from the turret without breakageor disturbing the printed coating.

The apparatus of our invention for printing workpieces has a frame, a carrier journaled on said frame, and a mo tion transmitting mechanism to intermittently index the carrier to advance workpieces held thereon from a loading station, to a printing station, and to a discharge station. At least one workpiece holder is mounted on the carrier. The workpiece feeding means is provided at the loading station with means to precisely locate the workpiece surface to be printed at a predetermined reference plane over the carrier for reception by the workpiece holder, The workpiece holder has a workpiece engagement means thereon for receiving a workpiece from the workpiece feeding means and preserving the predetermined reference plane of the workpiece surface to be printed. Printing means are provided at the printing station having at least one printing aperture. A means is provided for precisely positioning the printing means over workpieces held in the workpiece holder relative to the aforementioned predetermined reference plane. A workpiece removal means removes the workpieces at the discharge station.

The printing apparatus of our invention is capable of automatically and precisely printing workpieces at high volume rates. Further, the printing apparatus will consistently print coatings to uniform thicknessses on workpieces irrespective of minor thickness variations of the workpieces. This result is made possible because the apparatus of our invention locates the workpiece surface to be printed at a predetermined reference plane and maintains the surface in the reference plane during the printing operation. Minor thickness variations of the workpiece are accommodated by the workpiece holder. This same structure in our printing apparatus makes possible more accurate printing of workpieces that are slightly warped or bowed. Numerous safety devices can be incorporated into the printing apparatus to halt operation if a malfunction occurs. This prevents expensive delays and damage to the apparatus. At the discharge station, the printed workpieces are gently removed from the carrier without disturbing the printed coating. This operation is accomplished automatically without manual assistance. An indexing lock mechanism is also embodied in the printing apparatus of our invention which precisely positions the carrier to thereby accurately position a workpiece to be printed at the printing station. This index locking means will maintain the angular position of the carrier plate within the tolerances formerly believed impossible.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred specific embodiment of the invention as illustrated in the accompanying drawings.

In the drawings:

FIG. 1 is a pictorial view of a preferred specific embodiment of the printing apparatus of the invention.

FIG. 1A is a top plan view of the printing apparatus of the invention illustrating the various stations and their relative locations.

FIG. 2 is a top plan view of the workpiece holder.

FIG. 3 is a sectional view taken on line 33 of FIG. 2.

FIG. 4 is a pictorial view of the workpiece holder with parts omitted illustrating the clamping arm camming mechanism.

FIG. 5 is a side elevational view of the workpiece feeding mechanism for locating workpieces in the workpiece holder.

FIG. 6 is a detail view in broken section of the adjustable abutment means for limiting the stroke of the workpiece feeder plunger.

FIG. 7 is a top plan view in partially broken section illustrating the printing means.

FIG. 8 is a side elevational view in partially broken section of the printing means illustrating the adjustable mount of same.

FIG. 9 is a side elevational view of the unloading mechanism.

FIG. 10 is a top plan view of the unloading mechanism shown in FIG. 9.

FIG. 11 is a detail view showing the specific structure of the conveyor clutch utilized in the unolading mechanism.

FIG. 12 is a top plan view in broken section with elements and mechanisms removed illustrating the indexing lock mechanism used in the printing apparatus combination of the invention.

FIG. 13 is a detail view in broken section illustrating the retracted position of the detents in the unlocking mechanism.

FIG. 14 is a detail view in broken section illustrating the intermediate relative positions of the locking and locating detents of the locking mechanism.

FIG. 15 is a pictorial view illustrating the cam and cam follower mechanisms for actuating clamping arm and pedestal of the workpiece holder at the load and unload stations.

FIG. 16 is a schematic view illustrating the overall drive mechanism used to drive the various mechanisms of the printing apparatus.

FIG. 17 is a timing chart illustrating the correlation of the various elements and mechanisms of the printing apparatus during an indexing cycle.

Referring now to the drawings, FIGS. 1-17, there is depicted a preferred specific embodiment of the printing apparatus of our invention. As most clearly indicated in FIG. 1A, the printing apparatus basically has a rotatable carrier 32 provided with six indexable positions. A work holder 33 is mounted at each indexable position. However, any suitable number of indexable positions can be provided. Mounted around the carrier 32 is a workpiece feeding mechanism 20 constituting a loading station, a substrate presence detection means 22 constituting a substrate detection station, a printing mechanism 24 provided with a printing aperture 25 constituting a printing station, a workpiece unloader mechanism 26 constituting an unload station, and an indexer lock mechanism 30 for precisely positioning carrier 32 at each respective indexable position. Basically workpieces are fed into the loader mechanism 20 from a source 34. The workpieces are loaded onto the carrier 32 and held thereon by the workpiece holders 33. At the detection station 22 the workpiece detection means determines whether or not a workpiece is supported on the workpiece holder 33 under inspection. If it is determined that there is no workpiece in the holder, a circuit means and clutch will prevent the printing means 24 from operating when the carrier is indexed to the next position with the empty workpiece holder under the printing aperture. In operation the printing means 24 will imprint on the workpiece the desired design configuration. The indexer lock mechanism 30, positioned opposite the printing mechanism, precisely locates the carrier 32 so that the design configuration can be accurately imprinted on the workpiece. The unload mechanism 26 removes the imprinted workpieces from the carrier 32 and transfers them to a conveyor where they can be either stored in trays, moved to an oven for curing, or conveyed to subsequent processing apparatus.

In FIGS. 2-4 there is depicted a preferred specific embodiment of the workpiece holder 33 for use in the printing apparatus of our invention. The workpiece holder 33 has a base block 34 bolted to carrier 32. A vertically slidable spring-biased workpiece support pedestal 40 is mounted in block 34. Pedestal 40 has a generally planar top surface 41 preferably covered with a resilient material for direct engagement with the workpiece S. A vacuum supply passage 42 communicates with the top surface of the pedestal 40 which is connected to a source of vacuum which will be explained in detail in the operation of the unloader mechanism 26. On the lower portion of pedestal stern there is provided a telescoping connection consisting of a male portion 43 received in a female portion 44. Spring 45 spring biases portion 43 with respect to portion 44. The lower portion of the pedestal stern has a cam follower 46 which in operation is operatively engaged with a static cam 47 and a pedestal elevator 48 located at the loading station as more clearly indicated in FIG. 15. The cam follower portion 46 of the pedestal is biased downwardly by spring 40a as most clearly shown in FIG. 3. The lower end portion 43 of the pedestal stem is provided with a longitudinally extending slot 43a which receives pin 49 thus providing a slidable connection between the portions 43 and 44 of the stem of the pedestal 40. Pivotal clamping arms 50, each provided with two spaced pins 51 for engaging a workpiece S, are also mounted in base block 34. Pins 51 are preferably provided with a small groove 52 located at the approximate lower edge of a workpiece S positioned in the clamp arms. Groove 52 prevents the wearing of a shoulder in the pins which in operation might cause the workpiece to be cammed upwardly when the clamp arms are closed. The clamp arms 50 are actuated by a cam plate 53 having camming grooves 54 which receive cam followers 55 operatively connected to the clamp arms 50. The camming mechanism is most clearly illustrated in FIG. 4 of the drawings. In operation the camming plate 53 is rotated by cam follower arm 56 which in operation engages static cam 57 and earn arms 58 and 59, illustrated most clearly in FIG. 15 of the drawings. Tension spring 60 biases the cam plate 53 to cause clamp arms 50 to maintain a closed gripping position. A pedestal lock is provided to frictionally lock the pedestal 40 at preselected elevations. The pedestal lock consists of two lock plungers 61 slidably disposed in base block 34 normal to the axis of the pedestal stem, compression springs 62 biasing plungers inwardly so that the friction surfaces 63 are frictionally engaged with the stem of pedestal 40. An actuating cam 64 having fiat portion 65 is rigidly mounted on cam plate 53. In operation plungers 61 are held out of engagement with the pedestal stern except when the flat spots 65 are aligned with the cam follower surfaces 66 on the plungers.

The workpiece feeder mechanism 20 is illustrated most clearly in FIGS. 5 and 6 of the drawings. Feeder mechanism 20 has a workpiece feeder plunger 70 mounted for vertical movement on frame 71. A vacuum passage 72 connected to a source of vacuum terminates on the lower workpiece engaging face 73. Plunger 70 is reciprocated by plunger pivot arm 74 connected to rod 75, which is cam actuated by the drive mechanism of the printing apparatus. Workpieces S, generally referred to as substrates, are conveyed to substrate feeder plunger 70 on a chute 76. A belt conveyor 77, in combination with an idler wheel 78 for applying a downward force, gently urges substrates to the terminal end of chute 76. A photocell 79 can be provided to detect whether or not there is a supply of substrates. Suitable circuitry is provided which will shut down operation of the printing apparatus in the event that the supply of substrates is interrupted.

An adjustable plunger abutment mechanism for precisely locating the downward movement of plunger 70 is illustrated in FIG. 6. The abutment means consists of a longitudinally extending slot 105 in plunger 70 receiving a fixed abutment wedge 106 in engagement with a slidable wedge 107. Compression coil springs 108 maintain wedges 106 and 107 in snug engagement. An adjustment screw .109 is operatively connected to slidable wedge 107 to position it longitudinally relative to wedge 106. As will be appreciated movement of wedge 107 can be used to precisely adjust the top surface of wedge 106 which abuts the upper end of slot 105 and determines the downward limit of plunger 70.

In operation the substrate feeder mechanism supplies substrates S through chute 76 to the lower substrate engaging surface 73 of plunger 70. When plunger 70 is raised to the up position, the end substrate is moved outwardly underneath the ram 70 until it comes into abutment with stop 110. Vacuum applied through passage 72 prevents the substrate S from falling as it is moved into position. With the carrier 32 indexed to position the workpiece holder 33 underneath plunger 70, the plunger is moved downwardly with the end substrate held thereon. The substrates S in the chute are prevented from moving outwardly because the end substrate comes into abutment with recess 111 on the plunger 70.

In the aforementioned loading operation cam arm 58 engages the cam follower 56 thus opening the clamping arms 50 of the substrate holder 33. Almost simultaneously the pedestal elevator 48 engages cam follower 46 to urge the pedestal 40 upwardly beyond the clamping arms 50'. Plunger 70 with a substrate held thereon is then moved downwardly against the spring-biased pedestal 40 until the movement of plunger 70 is halted by the abutment means contacting slot 105. The clamping arms 50 are then closed into gripping engagement with the substrate, while simultaneously the plunger locks the elevation of pedestal 40. The plunger 70 is then withdrawn and the carrier 32 indexed to the next position. This operation accurately positions the top surface of the substrate to be imprinted at a predetermined reference plane governed by the plunger abutment means.

The printing mechanism 24 is illustrated in detail in FIGS. 7 and 8 of the drawings. Printing mechanism 24 has an inkwell 115 provided with an annular depression wit-h a bottom surface 135. The inkwell 115 is located with the portion embodying the printing aperture 25 overlying carrier 32. Printing aperture 25 in practice consists of a suitable mask having the desired design configuration mounted on a slide element 116. The mask and slide element 116 form a part of the floor 135 of the annular depression of inkwell 115. Inkwell 115 is mounted on a support plate 117 which is in turn pivotally supported by hinges 118. Hinges 118 consist of a flexible metal or steel strap rigidly bolted at one end to support plate 117 and at the other end to the stage mount assembly 120. Hinges 118 support the inkwell support plate 117 for pivotal movement without exhibiting looseness which might cause misalignment of the printing mask. Pivot links 119 connected to plate 117 and cam actuated by the driving mechanism of the printing apparatus pivot inkwell into and out of printing position. The plane that the inkwell 115 and the plane of the critical bottom surface of the attached printing mask assume during the printing operation are determined by a three point abutment consisting of a first ball abutment means 121 and two flat abutment means 122 shown in FIG. 7. The three point or triangular configuration placement arrangement of the abutment means supports the plate and inkwell 115 without tilting or rocking. Mounted for rotation in the inkwell 115 is a spider element 123 provided with a plurality of arms. Preferably the number of arms corresponds to the number of workpiece holders on the carrier 32. A squeegee element 123a (FIG. 1) is mounted in each of the arms of spider 123. Squeegees 123a move the printing ink or paste over the printing aperture and thereby cause the desired pattern to be printed on the substrate. Spider 123 is driven by the drive mechanism of the printing apparatus through a drive shaft embodying a spline and two spaced universal couplings (not illustrated).

The inkwell 115 and its supporting plate 117 are mounted on a movable stage so that it can be adjusted in the X and Y direction, and also angularly to position the mask in the precise location over the workpiece substrate holder 33 located at the printing station. The mount assembly consists of three separate plates 124, 125 and 126 as illustrated most clearly in FIG. 8 of the drawings. Preferably the plates are of a generally U-shaped configuration with a base thereof located beneath the hinges 118. The total thickness of plates 124, 125 and 126 is such as to locate the support plate 117 for inkwell 115 at approximately the right location to position the printing aperture 25 over the substrate holder 33. Plate 124 has mounted thereon a block 127 supporting hinges 118. On the top of plate 124 are mounted vertical guides 128 which slidably engage the pivotal end of support plate 117 to further insure that there is no sideways movement. A guide means is provided between plates 124 and 125 to allow sideways movement of plate 124 relative to plate 125. The guide means consist generally of a pair of slides 130 secured to plate 124 which are disposed in grooves 131 in plate 125. Ball bearings 132 reduce the sliding friction of the slides in the grooves. A similar set of guide means is provided between plates 125 and 126 which are disposed in a direction transverse to the aforementioned guides. With this assembly the inkwell 115 can be moved in either the X or the Y direction with adjusting screws 133. The bottom plate 126 is supported on the frame 36 for angular movement about pivot 134, and adjustment screw 135 provided to move same.

A spring-biased bearing assembly is mounted in plates 124, 125 and 126 to facilitate their movement relative to each other and to the base 36 during adjustment. The bearing assembly is illustrated in FIG. 8 of the drawings and consists of a recess 139 slidably receiving plug 136, bearing 137, and biasing spring 138. Similar bearing assemblies are positioned on each of the four corners of the respective plates. In operation the bearing assemblies: rollably support the respective plates thus making rela tive movement substantially friction free. In operation clamping bolts 140 are loosened through a suitable cam ming arrangement (not shown), the plates adjusted by moving adjustment screws 133 and 135, and the clamping bolts again tightened. The bearing assembly permits the plates to be securely clamped together without imposing great pressures on the bearing assembly.

The substrate detection means 22, shown in FIG. 1A, in operation detects whether or not there is a substrate located in the holder. If there is no substrate in the holder, 2. suitable circuit in combination with a clutch deactivates the printing assembly when the empty holder is indexed to the printing station. Thus, the spider 123 is not rotated and the inkwell is not pivoted downwardly in position over the substrate.

The unloader mechanism 26 is illustrated in detail in FIGS. 9, 10 and 11 of the drawings. Unloader 26 has a slide or chute 150 having a terminating end 151 positioned adjacent a workpiece holder 33, when located at the unloading station. The height of the terminal end 151 is the same as the height of the pedestal 40 of the workpiece holder 33 when the pedestal is in fully extended up posi tion. A conveyor having a belt 152 with cogs 153 is disposed over the chute 150 and extends over the workpiece holder 33. Belt 152 is entrained over pulleys 154 and 155 as indicated in FIG. 9. The belt 152 is driven by pulley 155 in turn connected to driving shaft 156 which is connected through a clutch 157 to the drive mechanism of the printing apparatus. In the clutch 157, driving torque is applied to pulley 158 by belt 159, in turn connected to the driving mechanism of the printing apparatus. Pulley 158 has a flange 158a having disposed therein ball receiving indentations 160. A hub 161 is keyed to shaft 156- and has a flange 162 disposed adjacent the flange 158a. Spring biased balls 163 are seated in apertures in flange 162 as indicated in FIG. 11. Located adjacent hub 161 is a second hub 165 that is spring biased into engagement with hub 161 by spring 166. Hub 165 has a flange 167 positioned adjacent the microswitch 168. Pins 170 are disposed between the balls 163 and flange 167 or hub 165.

In normal operation torque is transmitted from pulleys 158 to hub 161 which is keyed to the driving shaft 156 of pulley 155. However, if a malfunction occurs wherein the torque is sufficient to displace balls 163 from the depressions 160 in flange 159, pins 170 force hub 165 longitudinally which actuates microswitch 168. Activation of microswitch 168 shuts down the driving mechanism of the printing apparatus.

In operation carrier 32 moves the workpiece holder 33 into the unloading station. At the unloading station the pedestal elevator 172 is moved upwardly, spring biasing pedestal 40 upwardly. Simultaneously, cam actuator arm 59 engages the cam follower arm 56 and opens the clamping arms 50 of workpiece holder 33 and also cams plungers 61 away from the pedestal stem. Subsequently, the substrate held on pedestal 40 is elevated to the same elevation as the terminal end 151 of chute 150. The timing of the conveyor belt 152 is such that a cog 153 immediately sweeps the substrate S from the pedestal 40 onto the chute 150. A conveyor 173 then moves the unloaded substrate off to storage or other processing equipment. Vacuum is applied to the pedestal 40 to hold the substrate thereon prior to moving the carrier to the unload station. As indicated in FIG. 12 of the drawing, there is provided a slide valve disposed about the axis of carrier 32. The slide valve includes a stationary elongated arcuate slot 174 that is connected to a source of vacuum. Passages 174a, in communication with passage 42 in holder 33, of the respective holders are placed in register with slot 174 as holders are indexed by the carrier to the unload station. Photocell 175 can be provided to detect a back-up of substrates on conveyor 173. In the event that there is a back-up, the driving mechanism of the printing apparatus will be interrupted thereby preventing damage to the conveyor and to substrates positioned on the conveyor.

The carrier 32 is precisely positioned after each indexing movement by the indexing lock mechanism 30 shown in detail in FIGS. 12, 13 and 14. As indicated in FIG. 1A, the indexing lock mechanism is positioned opposite the printing means 24 and operates to consistently and securely locate the carrier and the workpiece holder beneath the printing aperture 25.

Carrier 32 is provided with detent engagement means on the peripheral edge in the form of hardened steel inserts 80 having a locator detent contact surface 81 and a locking detent surface 82. Preferably the detent engagement means are two spaced notches in the carrier. A separate pair of notches provided with the aforementioned contact surfaces can be provided, or alternately, notches can be positioned between the various locations to be looked, as illustrated in FIG. 12, wherein the front and trailing edge surfaces are used for sequential locking operations. A longitudinally slidable locator detent 83 is slidably supported in 'base 84. Locator detent 83 has a positioning surface 85 adapted to selectively engage contact surface 81 in the insert 80. As indicated in FIG. 12, the angle of detent surface 85 with respect to the longitudinal axis of locator index 83 is three degrees. The contact surface 81 is complementary to surface 85 on detent 83 when the carrier is in locked position. The reason for the angle of the surfaces will become more .apparent in the description that follows. An abutment is provided on detent 83 in the form of a lug 86 slidable in slot 87. Lug 86 limits the longitudinal movement of detent 83 and determines the exact seated position of the detent. A longitudinally slidable locking detent 88 having a wedging surface 89 is slidably mounted in base 84. As indicated in FIG. 12 the angle of the wedging surface 89 relative to the longitudinal axis of detent 88 is five degrees. Contact surface 82 on insert is complementary to surface 89 when the carrier 32 is in indexed or locked position.

A detent actuating mechanism moves the locator detent 83 into engagement with the detent abutment means in advance of moving the locking detent 88 into wedging engagement with the locking detent contact surface 82. The detent actuating mechanism consists of longitudinally extending recesses 90 in each of detents 83 and 88. A slide element 91 is slidably disposed in the recess 90. A spring 92 is also positioned in each recess 90 having one end in engagement with the end of the recess and the other in biasing engagement against the slide 91. Springs 92 are loaded so as to force the slides 91 against the opposite ends of recesses 90 when the respective detents are in unactuated or non-locking position, illustrated in FIG. 13. Slide element 91 includes a rod 93 rigidly joined to a crossbar 94. A suitable linkage (not shown) applies a force against crossbar 94 which in turn forces the detents 83 and 88 into locking position. Crossbar 94 is actuated by a suitable cam or other actuating means correlated with the indexing drive for carrier 32. Any suitable cam or other actuating means can be utilized and will not be described in detail. Any suitable biasing arrangement can be used to move the detents into engagement that achieves the desired mode of operation. For example, the detents can be resiliently biased into engagement by a pair of arms mounted on a pivotable shaft.

In FIG. 13 the detents 83 and 88 are shown in unengaged or non-locking position. FIG. 14 illustrates the relative position of the detents and inserts 80 on carrier 32 at an intermediate stage of the locking operation, that is with locating detent 83 in seated position and locking detent about to advance into wedging engagement. FIG. 12 illustrates the detents in the fully locked position. In the unlocked position, illustrated in FIG. 13, crossbar 94 is in the retracted position and the slides 91 are biased by springs 92 to the rear end of recesses 90. In this relative relationship the leading carrier engaging end of detent 83 is advanced relative to the engaging end of detent 88. Preferably, in operation locator detent 83 is moved into seated position with lug 86 in abutting relation slightly before the carrier is rotated to the indexed position. Normally, the driving mechanism of the carrier moves the carrier just short of the index position, and the detent 88 completes the rotation. Therefore, the timing of the movement of crossbar 94 to urge detent 83 outwardly is such that sliding friction between surfaces 81 on the insert and on the detent is avoided because detent 8.3 is extended just before the carrier is rotated to put the surfaces into abutting engagement. The relative positions of detents 83 and 88 and the carrier 32 at this point are illustrated in FIG. 14 of the drawings. Note that detent 88 lags behind detent 83. As the advancing of crossbar 94 continues, spring 92 in detent 83 is compressed while spring 92 in detent 88 is not because detent 88 has not encountered any significant opposition. As the advancing movement of crossbar 94 continues, wedging surface '89 will come into wedging contact with contact surface 82. on insert 80 thus urging surface 81 of insert 80 against surface 85 of detent 83. Ultimately both detents are firmly placed in engagement with the respective surfaces of inserts '80 thereby accurately positioning the carrier 32 in the index position. The angle of locating surface 85 on locator detent 83 is less than the angle of wedging surface 89 on locking detent 88 to prevent detent 83 from being forced backward out of seated relationship by the wedging action of detent 88.

In order to further improve the efiiciency and effectiveness of the indexing lock of the invention, the detents 83 and 88 can be supported on bearing means. An embodiment of the bearing means is illustrated in FIG. 12. Detents 83 and 88 are provided with grooves in the edges thereof which serve as braces for ball bearings. Ball bearings 95 are seated in slots 96 in base 84. A spring-loaded bearing assembly is provided on the carrier engaging end of each of the detents opposite the insert engaging surfaces. The spring-loaded bearing consists of a recess 97 having a plug 98 slidably disposed therein, a spring means 99 urging the plug 98 toward the detent, and the ball bearing 100. As indicated in FIG. 12, the spring-loaded bearings should be positioned adjacent the locking ends of the detents opposite the insert or notch engaging surfaces thereof. Similar spring-loaded bearing assemblies can be provided on the opposite ends of the detents on the opposite side edges.

In operation, as detent 83 is urged into position into locating engagement with insert 80, the bearings, previously described, support the detent for sliding engagement out of contact with the surfaces of base 84. However, upon completion of the wedging engagement of the locking detent 88, wherein the surface 85 of the detent is forced against the surface 81 of the insert, the spring loaded bearing 100 is forced inwardly placing the surface 101 of detent 83 in firm abutting engagement with the corresponding slide surface of base 84. This surface contact is achieved after the detent 83 is moved longitudinally into its seated position in insert 80. Therefore, there is virtually no sliding friction which can cause wear and the like.

In FIG. 16 is shown a schematic drawing of the driving mechanism for the printing apparatus of the invention. The driving mechanism has a motor 180 connected to an electromagnetic clutch-brake 181. The clutch-brake 181 is actuated by the various safety mechanisms, as for example photocell 79 of the loader mechanism 20, and the photocell 175 in the unloader mechanism 26. The output shaft of clutch-brake 181 is connected in operative driving engagement to a worm gear speed reducer 182. The output of the reducer 182 is connected to a cam mechanism 183 that actuates pedestal elevator 172 and camming arm 59 at the unload station. Mechanism 183 includes a drive shaft 195 for unloader 26. The output of reducer 182 also is connected to the carrier drive indexing means 184 that provides the indexing movement of carrier 32. The output of reducer 182 is also connected to a cam mechanism 185 which drives pedestal elevator 48, a cam driving rod 75 for actuating loading plunger 70, and camming arm 58 at the loading station. The torque for worm gear reducer 182 is also transmitted to a single revolution clutch mechanism 186 for driving the printing means 24. Clutch 186 is selectively activated by the substrate detection means 22. In the event that detection means 22 detects the absence of a substrate in work holder 33, the clutch 186 is activated during the next indexing movement of the carrier which thereby prevents the printing apparatus from operating. The output of clutch 186 is transmitted to cams 187 which operatively engage cam followers operatively connected to camming links 119 that pivot the inkwell into and out of printing position.

The output of clutch 186 also drives a worm gear drive 188 which rotates the spider 123 of the printing apparatus 24. Motor also drives through clutch brake 181, shaft 190 which rotates a cam 191 that operates the indexing lock mechanism 30, and also an electrical circuit breaker 192.

FIG. 17 is a timing chart which illustrates the correlation of the various cam actuated elements of the printing apparatus that are driven or actuated by the drive mechanism illustrated in FIG. 16 of the drawings. In FIG. 17 a complete indexing cycle is represented on the ordinate as 360 degrees. This cycle corresponds to a total angular rotation of the carrier of 60 degrees when six work holders are provided thereon.

Curve a depicts the movement of cam arm 59 for actuating the clamp arms 50 of the work holder at the unload station. A comparison of curve h which depicts the movement of the index drive mechanism of the printing apparatus indicates that the cam arm 50 moves to a retracted position during movement of the carrier plate. Camming arm 56 moves off the cam arm 59 during the carrier movement into engagement with static cam 57 as indicated in FIG. 15. Cam arm 59 is moved to the closed position, that is in a position with respect to cam follower arm 56 that does not move arm 56 contrary to the biasing of spring 60, in order to place same into position to receive the next cam actuator 56 of the workpiece holder as it approaches the unload station. As curve a further indicates, the cam arms are subsequently opened by the cam arm 59 after the carrier has arrived at the unload station. Curve b depicts the movement of pedestal elevator 172. As indicated the pedestal 40 of the workpiece holder is moved upwardly after the clamp arms have been opened as indicated by curve :1.

Curve 0 depicts the movement of the load plunger 70 of the loader mechanism. Curve d depicts the movement of the cam arm 58 which actuates the clamp arms 50 of the workpiece holder 33 at the load station. As indicated cam arm 58 is moved into the open position during indexing movement of the carrier plate so that cam actuator 56 in engagement with static cam 57 will roll smoothly into engagement with the cam arm. A comparison of curves d and 0 indicates that the clamp arms are closed after the load plunger 70 is moved into the down position to thereby locate the upper surface of the substrate. Curve e indicates the movement of the elevator cam 48 at the load station which actuates the pedestal 40. As indicated the pedestal 40 is biased upwardly during the downward movement of load plunger 70 as indicated by curve c.

Curve 1 indicates the movement of cam 187 which moves the inkwell into and out of printing relation with the substrates at the printing station. Curve g indicates the movement of cam 191 which actuates the index lock mechanism. Note that the carrier plate is looked a short interval before and after the period that the substrates are screened.

While the invention has been particularly shown and described with reference to a preferred specific embodiment thereof, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.

We claim:

1. Apparatus for printing workpieces comprising,

a frame,

a carrier journaled on said frame,

at least one workpiece holder mounted on said carrier,

motion transmitting mechanism to intermittently index said carrier to advance workpieces in said workpiece holder from a loading station, to a printing station, and to a discharge station,

workpiece feeding means at said loading station having means to contact at least a portion of the workpiece surface to be printed and thereby precisely locate said surface at a predetermined reference plane over said carrier for reception by said workpiece holder,

workpiece engagement means on said workpiece holder for receiving a workpiece from said workpiece feeding means and preserving the predetermined reference plane of the workpiece surface to be printed irrespective of workpiece thickness irregularities,

printing means at said printing station having at least one printing aperture,

means for precisely positioning said printing means over a workpiece in said workpiece holder relative to said predetermined reference plane, and

workpiece removal means at said discharge station.

2. The apparatus of claim 1 wherein said workpiece feeding means comprises a workpiece slide conveyor having a generally horizontal portion terminating over said carrier.

3. The apparatus of claim 2 wherein said means to precisely locate the workpiece surface of said workpiece feeding means comprises, a vertically reciprocatable plunger located at the terminal end of said slide conveyor and having a lower surface adapted in use to contact the upper surface of a workpiece to be printed, abutment means to precisely limit the downward movement of said plunger, and means to reciprocate said plunger in synchronism with the indexing motion of said carrier.

4. The apparatus of claim 3 wherein there is provided an aperture in the lower surface of said plunger of said workpiece feeding means, a source of vacuum in communication with said aperture.

5. The apparatus of claim 2 wherein said feeding means comprises, a vertically reciprocal plunger located over said carrier at the end of said workpiece slide, and a means to hold workpieces to be positioned on said plunger.

6. The apparatus of claim 5 wherein said workpiece holder comprises, gripping means for selectively engaging the edges of a workpiece, means for moving said gripping means into and out of engagement with a workpiece, a vertically reciprocal pedestal for supporting a workpiece in engagement with said gripping means, and a means to elevate said pedestal to adjustably receive and support a workpiece to be printed from said plunger means of said workpiece feeding means.

7. The apparatus of claim 6 wherein there is provided a lock means for maintaining the adjusted elevation of said pedestal.

8. The apparatus of claim 7 wherein said gripping means is comprised of spaced locator arms, each of said arms provided with spaced locating pins for locating and engaging the edges of a workpiece, and said means for actuating the gripping means is a rotatable cam provided with parallel camming groove surfaces, and cam follower arms in sliding engagement with said camming groove surfaces and connected to each of said locator arms.

9. The apparatus of claim 7 wherein said lock means is comprised of at least one radially disposed spring biased lock plunger having an end thereof in frictional engagement with said pedestal, a locking cam follower surface on said lock plunger, and a rotatable locking cam in engagement with said locking cam follower adapted to cam said lock plunger outwardly out of engagement with said pedestal, said rotatable lock cam associated with said means for moving said gripping means.

10. The apparatus of claim 1 wherein said printing means is comprised of an inkwell having an annular shaped depression, a spider element having a plurality of radiating 'arms rotatably mounted over said inkwell, squeegee blades on said arms in wiping contact with the bottom surface of said depression of said inkwell, means for rotating said spider in synchronism to movement of said carrier, hinge means on said inkwell, and means for pivoting said inkwell into and out of printing position with said printing aperture over a workpiece supported in a workpiece holder at said printing station.

11. The apparatus of claim 10 wherein there is provided a workpiece detection station located between said loading station and said printing station, sensing means at said workpiece detection station for detecting the pres ence or absence of a workpiece in said workpiece holder when located at said detection station, and means to inhibit said means for pivoting said inkwell in response to said sensing means when there is an indication of workpiece absence.

12. The apparatus of claim 10 wherein said hinge means is comprised of at least one flexible spring element having an end rigidly afiixed to said frame and the other end rigidly aflixed to said inkwell.

13. The apparatus of claim 11 wherein there is provided three inkwell abutment elements for precisely locating the printing position of said printing aperture in said predetermined printing plane.

14. The apparatus of claim 1 wherein said printing means is comprised of, an inkwell, movable squeegee means in said inkwell, pivoted support for said inkwell, resilient hinge means pivotally supporting said support for said inkwell, three abutment means for limiting downward movement of said support for said inkwell, arranged in a triangular configuration, and means for pivoting said support for said inkwell into and out of abutting relation with said abutment means.

15. The apparatus of claim 14 wherein there is provided an adjustable stage for mounting said resilient hinge means comprised of, a first generally planar member supported on said frame, first guide means supporting said first member for horizontal movement, first adjustment means for moving said first member on said first guide means, a second generally planar member underlying said first member, second guide means supporting said second planar member for horizontal movement transverse to movement provided by said first guide means, and second adjustment means for moving said second member on said second guide means.

16. The apparatus of claim 15 wherein said adjustable stage mount includes a third generally planar member underlying said second member, a pivot means pivotally connecting said third member to said frame, and third adjustment means for pivotally moving said third plate about said pivot means.

17. The apparatus of claim 16 wherein there is provided spring biased bearing means for supporting said members comprising a plurality of recesses on the bottom side of said member, a plug slidably disposed in each of said recesses, a ball bearing in each of said recesses disposed in rolling contact with said plug, resilient means urging said plug against said ball bearings to thereby resiliently support said member.

References Cited UNITED STATES PATENTS 764,096 7/1904 Williams 101-407 1,533,700 4/1925 Dibbleet a1. 101-126 2,056,117 9/1936 Ziegler 101-407 2,398,658 4/1946 Mead 269157 XR 2,440,366 4/ 1948 Cropp 269-229 XR 2,555,204 5/1951 Sorrell.

2,601,826 7/1952 Huntar et al 101-35 2,648,139 8/ 1953 Wilkerson 248-349 XR 2,745,186 5/1956 Faeber 101-407 XR 2,966,115 12/1960 Arelt 101-126 3,067,496 12/1962 Rayburn 221-211 XR 3,180,255 4/1965 Christie 101-126 XR 3,263,603 8/1966 Fuchs 101-123 ROBERT E. PULFREY, Primary Examiner.

CLIFFORD D. CROWDER, Assistant Examiner.

US. Cl. X.R. 269-229; 221-211 

